Ref. 26 in the paper describes the PW laser. While that reference doesn't give an actual size for the thing, looking at the schematic it's probably a good-sized room filled with the necessary amplifier stages and so on.

Tabletop does seem to be hyperbole, but it's a big advance in itself that you can buy this hardware to install in an existing facility, rather than having to build the facility around the purpose of housing the laser.

Tabletop does seem to be hyperbole, but it's a big advance in itself that you can buy this hardware to install in an existing facility, rather than having to build the facility around the purpose of housing the laser.

Well, the point to the "tabletop" bit is that the accelerator itself really does fit on a tabletop. That alone is a significant advancement, and actually the notable bit about the whole thing (that they managed to perform the acceleration over a comparatively minuscule distance). Yes, it requires a powerful laser to work, but this was just an experiment to prove it can be done, not a test of a finished accelerator assembly.

Laser technology is constantly improving. It might take a laser the size of a large room to do this now, but in 10 years we might be able to do the same thing with something that can actually fit on a desktop. Lasers are something very many research facilities will already have or want for many reasons (albeit most don't have one on this scale quite yet), it's not like the laser is necessary for the accelerator and the accelerator alone (in contrast with the kilometer long assembles needed for previous methods).

No, this breakthrough doesn't mean in a few months you'll be able to fedex an X-ray laser to your lab, but this is the kind of breakthrough that could lead to exactly that.

I always thought something like this would make for an awesome roller coaster. Have it look like your coaster is going to collide with another on coming coaster then sharply veer away at the last minute. Depends would be on hand for riders.

Can you elaborate on how the electrons get accelerated? The light pulse liberates the electrons from successive nuclei in its path, correct? But on a gross scale the plasma is still electrically neutral. So how does there exist a gradient that causes acceleration in one direction?

Given the diminution of lasers over the last 2 decades it won't be long until the laser to drive this device is truly tabletop-sized.

Actually, the lasers which count (as far as this application is concerned) have not gotten any smaller in the last 20 years. The power supply has, perhaps, halved in size, but otherwise there has been very little change

Can you elaborate on how the electrons get accelerated? The light pulse liberates the electrons from successive nuclei in its path, correct? But on a gross scale the plasma is still electrically neutral. So how does there exist a gradient that causes acceleration in one direction?

Because in the process of creating the plasma you do not have charge neutrality of the width of the laser beam. The pondermotive force drives all the electrons to the outside, creating a bubble of positively charged material surrounded by a skin of electrons. The electrons are all accelerated towards the most positive part of the bubble. From the point of view of the electrons, the bubble is just behind the laser pulse, so it appears to move at the speed of light through the plasma (or close to it), so the electrons are always chasing that positive charge.

I haven't seen the news articles referenced, so maybe I don't completely understand what's going on here... but it sounds like this is a potential replacement for large national-scale particle accelerators? The kind that currently require *miles* of subterranean tunnels and equipment sometimes spanning multiple countries?

If that's the case, I think "tabletop" is a pretty reasonable description for a replacement that takes "2 or 3 heavily shielded rooms". Okay, maybe it's not perfectly literal, but this seems a little pedantic.

Article:You accelerate down the potential hill toward the waiting nuclei.

But by the time you get there, the light pulse has created even more attractive-looking nuclei in the distance—you know the sort, with a jacuzzi and a bit of backyard to call your own. The hill steepens and seems without end, and there is no other direction but down. You race on down the potential hill, still accelerating.

I don't get why, having reached a near nuclei, a distant nuclei should be more attractive. What makes the difference that pulls the electron away from the bird in the hand towards the ones out there in the bush?

To get to do an experiment at a free electron laser facility, you have to put in a proposal. Both you and the scientific staff at the facility have to agree that the experiment will generate something useful and interesting. That makes applicants think very hard about what sort of experiments they want to do. Unfortunately, this means they tend to choose relatively safe experiments. There are no Friday night, do-it-to-see-what-happens experiments at free electron laser facilities.

I really love that kinda articles - explaining complicated things that not-everyone-knows about in a way that curious people who are not physicist can understand. Also, shows that science doesn't have to be dead-serious all the time.

And as for the press-release exaggeration - that's why i tend to dislike journalism in general. People always go for the flashy titles, exaggeration and end up publishing bullshit. The other day i was "cited" in a local newspaper, and when i read the actual article i didn't quite remember having said the things they had written...

Oh well, at least some journalists keep it real, on some sites/medias...

Considering the fact that cyclotrons used for proton radiation therapy only produce particles in 100-300Mev range and take up most of a hospital basement, using the term "tabletop" isn't much of an exaggeration when one puts these things in perspective. Let's also not forget the fact that to produce energies in the Gev range normally will require superconducting magnets and all of the support infrastructure that goes along with that. So to say that the author is being pedantic about this is being charitable.